PSI - Issue 4

J. Maierhofer et al. / Procedia Structural Integrity 4 (2017) 19–26 Author name / Structural Integrity Procedia 00 (2017) 000–000

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residual stress influence on the crack growth threshold and rate.

Fig. 3. Influence of residual stresses on the crack propagation threshold and rate of EA4T in SE(B) specimens. (a) Residual stress distribution in axial direction across the specimen width, determined using the cut-compliance method. (b) Crack propagation rate in specimens with an initial crack size of 2 mm without (grey) and with residual stresses as in (a) (red), from Maierhofer et al. (2014b).

3.2. Overloads

Laboratory fatigue specimens are very often tested using constant loads, but in reality constant loads are the exception rather than the normal case. Real components are subjected to variable amplitude loading conditions, and within this variable amplitude loading sometimes very high loads (overloads) can occur. To investigate the influence of single compressive and tensile overloads on the crack propagation rate, again SENB specimens with the geometry shown in Fig. 1 were used. After pre-cracking, a constant amplitude cyclic load (high enough to lead to final fracture) was applied until a crack extension of ~4 mm was reached. Then a single overload was applied and the experiment was again continued using the primary load amplitude. In Fig. 4 the influence of a single compressive and tensile overload three times higher than the primary load amplitude is shown. The crack propagation rate is compared to a reference specimen were no overload was applied.

Fig. 4. Crack retardation due to single overloads: (a) compression overload; (b) tension overload.